Fusion of damaged or degenerated bones in joints is common in the orthopedic field. Joint fusion involves fixing two or more bones relative to one another so that they no longer move relative to one another. Joint fusion can be accomplished by securing the bones that are to be fused together using some type of appliance. In some cases, bones may simply be secured together using screws, while in other cases a plate or another appliance is used to stabilize the bones during the fusion process. Joint fusion may also involve packing bone graft material (e.g., fragments of bone removed from another location in the patient's body) between the bones of interest to facilitate a fusion process.
Joint fusion may be performed as a treatment for certain types of arthritis. For example, if arthritis of the wrist does not respond to other treatments, such as anti-inflammatory medication, application of splints, or steroid injections, a total wrist fusion may be performed in which the radius, most or all of the carpal bones, and one or more of the metacarpals are fused. However, total wrist fusion substantially diminishes function as it immobilizes virtually the entire wrist joint. Although total wrist fusion may be necessary to relieve chronic and severe pain from certain forms of arthritis, it is typically preferable to maintain as much natural motion of the wrist joint as possible.
Accordingly, limited wrist fusion may be the preferred treatment for certain types of arthritis. In limited wrist fusion, at least some of the bones of the carpus are fused together without fusing the metacarpals to the carpals or the radius to the carpals. One common limited wrist fusion procedure for patients with advanced degenerative change in the wrist is known as “four corner” fusion. Four corner fusion involves fusing the capitate, hamate, lunate, and triquetrum bones in the carpus to reduce pain from the joint while still preserving some motion. Four corner fusion may be used, for example, to treat scapholunate advanced collapse (SLAC wrist) or scaphoid nonunion advanced collapse (SNAC wrist). Four corner fusion may also be used to treat other conditions, such as trans-scaphoid perilunate fracture dislocation.
Four corner fusion may be performed simply using screws to secure the capitate, hamate, lunate, and triquetrum bones together. Overall stability can be improved, however, using an appliance that is secured to the carpus bones using screws. Moreover, such an appliance can serve as a guide for appropriate placement of screws, which can make the procedure easier to perform.
One appliance for use in four corner fusion is disclosed in U.S. Pat. No. 6,179,839 B1, issued to Weiss and Collins. The '839 patent discloses a four corner fusion apparatus that comprises an annular plate with a substantially conical shape having a top outer edge of greater diameter and a smaller diameter inner bottom edge. A conical burr is used to rasp out a conical cavity at the juncture of the capitate, hamate, lunate, and triquetrum bones. The conical, annular plate is then placed in the resulting conical cavity and bone screws are inserted through apertures in the plate into the capitate, hamate, lunate, and triquetrum bones and tightened to pull the bones together.
Another appliance for use in four corner fusion is disclosed in U.S. Patent Publication No. 2006/0025772, filed by Leibel, Cooney, Linscheid, and Berger. The '772 publication discloses a carpal compression plate for use in four corner fusion. The carpal compression plate has a concave profile and a diamond shape, and is described as having a low profile that reduces the amount of bone resection relative to the appliance disclosed in the '839 patent. The plate includes four screw apertures, at least one of which is elongate and is narrower at a peripheral end and countersunk or otherwise shaped to be broader at a central end. As one or more the screws are tightened into the elongated screw apertures, they tend to migrate from the more peripheral portion of the elongated aperture to the more central portion, drawing the bones attached to these screws to be fused tightly together. In addition, a multi-lobate central aperture is intended to provide ease of access to the joint space between the capitate, hamate, lunate, and triquetrum bones after fixation of the fusion plate to allow easier placement of bone graft.